This article provides an overview of the neuroimaging literature focused on preoperative prediction of meningioma consistency. A validated, noninvasive neuroimaging method to predict tumor consistency can provide valuable information regarding neurosurgical planning and patient counseling. Most of the neuroimaging literature indicates conventional MRI using T2-weighted imaging may be helpful to predict meningioma consistency; however, further rigorous validation is necessary. Much less is known about advanced MRI techniques, such as diffusion MRI, MR elastography (MRE), and MR spectroscopy. Of these methods, MRE and diffusion tensor imaging appear particularly promising.
Key points
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There are currently no validated neuroimaging techniques to predict preoperative meningioma consistency.
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T2-weighted imaging evaluation is relatively straightforward and may be useful. However, further validation is needed.
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Little is known about advanced MRI techniques, such as diffusion MRI, magnetic resonance (MR) elastography (MRE), and MR spectroscopy. Of these techniques, MRE and diffusion tensor imaging appear particularly promising.
Introduction
Meningioma is the most common primary brain tumor. With surgery being a primary mode of therapy, minimally invasive alternatives to conventional open approaches to the resection of intracranial meningiomas, such as keyhole or endoscopic transnasal approaches, have recently become more commonplace in tumors of the skull base. However, proper patient selection is critical to determine which neurosurgical operation is most appropriate for a given patient. Multiple factors, such as tumor location, invasiveness, encasement of vital structures, and vascularity, must be taken into consideration. Tumor consistency, also referred to as firmness or texture, is another factor that has been increasingly recognized as an important criterion to consider before a meningioma operation. Multiple reports have described the significance of a meningioma’s consistency to determine surgical planning and expectations regarding the extent of resection. Furthermore, this information can be very helpful when patients are counseled regarding potential risks and length of operating time. This is particularly true for tumors that demonstrate extremes of consistency (ie, extremely soft vs extremely firm). Although it appears that water and collagen content are important determinants of meningioma consistency, no definite association with histopathological subtype has been established. This review summarizes the current neuroimaging literature as it relates to the preoperative evaluation of meningioma consistency.
Introduction
Meningioma is the most common primary brain tumor. With surgery being a primary mode of therapy, minimally invasive alternatives to conventional open approaches to the resection of intracranial meningiomas, such as keyhole or endoscopic transnasal approaches, have recently become more commonplace in tumors of the skull base. However, proper patient selection is critical to determine which neurosurgical operation is most appropriate for a given patient. Multiple factors, such as tumor location, invasiveness, encasement of vital structures, and vascularity, must be taken into consideration. Tumor consistency, also referred to as firmness or texture, is another factor that has been increasingly recognized as an important criterion to consider before a meningioma operation. Multiple reports have described the significance of a meningioma’s consistency to determine surgical planning and expectations regarding the extent of resection. Furthermore, this information can be very helpful when patients are counseled regarding potential risks and length of operating time. This is particularly true for tumors that demonstrate extremes of consistency (ie, extremely soft vs extremely firm). Although it appears that water and collagen content are important determinants of meningioma consistency, no definite association with histopathological subtype has been established. This review summarizes the current neuroimaging literature as it relates to the preoperative evaluation of meningioma consistency.
Reference standards of meningioma consistency
Before delving into the neuroimaging aspects of meningioma consistency determination, it is necessary to consider what reference standards are being used when a neuroimaging method is being evaluated for its discriminative ability. In 2013, Zada and colleagues proposed a meningioma consistency grading system based on an ordinal scale rather than simply labeling meningiomas as either “soft” or “hard.” The impetus for their approach was due to the common practice in neuroimaging studies of retrospectively using this binary approach based on neurosurgical operative reports, a method that also failed to recognize areas of mixed consistency within the tumor. Their 5-point scale was based on the surgeon’s ability to internally debulk the meningioma as well as the ease with which the tumor capsule could be folded after debulking. A grade of 1 corresponded to an extremely soft tumor that required only suction for internal debulking and either had no capsule or the capsule was easily folded. At the other extreme, a 5 represented a calcified, extremely firm tumor with a density that was close to that of bone and whose rigid capsule did not allow for collapse or folding. Debulking of these tumors was difficult despite the use of ultrasonic aspiration, cautery loop, or sharp/mechanical dissection. Using this scale, 2 neurosurgeons independently evaluated 50 consecutive patients with meningioma who underwent surgical resection in a prospective fashion. The investigators found that this proposed grading system resulted in a high degree of user agreement between the 2 surgeons for overall tumor consistency. The investigators of a very recent neuroimaging study of meningioma consistency felt that the Zada classification resulted in less variability and subjectivity compared with a neurosurgeon’s qualitative assessment of “hard” versus “soft.” Utilization of grading schemes such as those proposed by Zada and colleagues may allow for more objective comparison of studies examining meningioma consistency.
Neuroimaging studies of meningioma consistency
There have been a variety of neuroimaging approaches that have sought to predict meningioma consistency. However, there have been conflicting results and no universally accepted method has been established to date. These studies have used imaging approaches ranging from conventional imaging (MRI, computed tomography [CT]) to the application of advanced MRI techniques ( Box 1 ).
Conventional MRI: mainly T2-weighted imaging
Diffusion MRI: diffusion-weighted imaging and diffusion tensor imaging
Magnetic resonance (MR) spectroscopy
MR elastography
Dynamic contrast-enhanced MRI
Magnetization transfer MRI
Conventional computed tomography
Conventional MRI
Most of the literature concerned with imaging prediction of meningioma consistency has used conventional MRI techniques. Table 1 provides on overview of these studies. To the best of our knowledge, the earliest of these was that by Chen and colleagues from our institution. Their retrospective study of 54 patients found that hyperintensity on T2-weighted imaging (T2WI) relative to gray matter was associated with soft tumor consistency. On the other hand, T1-weighted imaging (T1WI) had no association with consistency. Indeed, multiple other studies have shown that there is an association between signal intensity on T2WI and meningioma consistency. The hyperintensity on T2WI of soft tumors may be related to higher water content, whereas the lower signal on T2WI for hard tumors might be due to less water and more collagen and calcium content. Increased cellularity is also thought to play a role in decreasing signal intensity on T2WI. Its interaction with fibrous content and interstitial fluid, which may increase signal intensity on T2WI, can affect signal intensity in a complex manner that could limit diagnostic accuracy of meningioma consistency prediction.
| Author, Year | No. of Cases | Association Between Conventional MRI and Consistency? | Method of MRI Signal Intensity Determination | Reference Standard for Consistency |
|---|---|---|---|---|
| Chen et al, 1992 | 54 | Yes, T2WI | Visual | Operative report, described as “soft” or “firm” |
| Carpeggiani et al, 1993 | 43 | No | Visual | Operative and pathologic report, described as “soft,” “hard,” or “mixed” |
| Suzuki et al, 1994 | 73 | Yes, T2WI | Visual | Operative report and video recordings taking into consideration surgical instruments, described as “soft,” “moderate,” or “hard” |
| Yamaguchi et al, 1997 | 50 | Yes, T2WI and PDWI | Visual | Intraoperative based on surgical instruments used, described as “soft,” “mixed,” or “hard” |
| Maiuri et al, 1997 | 35 | Yes, T2WI | Visual | Pathologic report examining histologic subtype |
| Yrjänä et al, 2006 | 21 | Yes, T2WI | Relative signal intensities were created by dividing tumor signal intensity by cortical gray matter | Intraoperative based on visual analog scale |
| Kashimura et al, 2007 | 29 | No | Visual | Intraoperative based on surgical instruments used, described as “soft” or “hard” |
| Kim et al, 2008 | 27 | Yes, T2WI | Visual | Intraoperative findings, described as “friable soft” or “hard” |
| Hoover et al, 2011 | 101 | Yes, T1WI and T2WI | Visual | Operative report, described as “soft and/or suckable” or “firm and/or fibrous” |
| Chernov et al, 2011 | 49 | Yes, T2WI | Visual | Intraoperative based on instruments used, described as “soft,” “mixed,” or “hard” |
| Sitthinamsuwan et al, 2012 | 243 | Yes, T2WI and FLAIR | Visual | Intraoperative based on instruments used and video recordings, described as “soft,” “intermediate,” or “hard” |
| Romani et al, 2014 | 110 | No | Visual | Intraoperative assessment based on surgical instruments used and tactile sense, described as “soft,” “medium,” or “hard” |
| Ortega-Porcayo et al, 2015 | 16 | Yes, T1WI and T2WI | Visual | Intraoperative assessment using Zada et al grading system and dichotomous “soft” or “hard” grading |
| Smith et al, 2015 | 20 | Yes, T2WI | Used T2WI to create tumor to middle cerebellar peduncle ratios | Intraoperative assessment based on Cavitron Ultrasonic Surgical Aspirator intensity to designate tumors as “soft,” “intermediate,” or “firm” |
| Watanabe et al, 2015 | 43 | Yes, T2WI, FLAIR, contrast-enhanced FIESTA | Created signal intensity ratio by comparing tumor to cerebral cortex | Intraoperative based on visual analog scale |
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